The present invention relates to a method for controlling the distribution of spark voltages to multiple cylinders of a combustion engine and, in particular, to a method for controlling the rotation speed of the rotatable electrode of a spark voltage distributor associated with an ignition coil and multiple spark plugs.
In a multi-cylinder combustion engine, combustible mixtures supplied to multiple cylinders are sequentially ignited by respective spark voltages generated by an ignition coil and distributed to multiple spark plugs to rotate the engine output shaft which responsively produce an output torque. The timing of spark ignition must be controlled in response to changes in the operating conditions of the combustion engine to increase the engine output torque, or operate the engine at the possible highest efficiency. For this reason it is desirable to associate with the engine an electronic spark ignition control system in which spark voltage generation of the ignition coil is controlled electronically. Even with the electronic spark ignition control system having a capability of precise ignition timing control, spark voltages generated by the ignition coil must be distributed to the respective spark plugs.
It is general to associate with the ignition coil and the spark plugs a spark voltage distributor having a rotatable electrode connected to the ignition coil and stationary electrodes to the respective spark plugs. With the rotatable electrode being coupled to the engine output shaft to rotate therewith, the spark voltage distributor is enabled to distribute the spark voltages to the respective spark plugs upon engagement of the rotatable electrode with the stationary electrodes which are spaced from each other and encircle the rotatable electrode. The spark voltage distributor mechanically coupled to the engine output shaft is not advantageous in that the distributor is necessarily mounted close to the engine output shaft and that, when the timing of spark voltage generation is advanced greatly, the spark voltages are likely to be distributed to improper spark plugs due to flash-over of the spark voltages which occurs between the rotatable electrode and the stationary electrodes disengaged from the rotatable electrode. As to flashover of the spark voltages, it occurrs more frequently when the number of stationary electrodes, or the number of engine cylinders, increases to result in narrowed spacing between stationary electrodes.